It is known in the automotive industry to provide for wireless monitoring of vehicle tire parameters, particularly tire pressure. In such tire pressure monitoring systems, tire pressure sensors and radio frequency (RF) transmitters are mounted inside each tire, typically adjacent the inflation valve stem. In each tire, the tire pressure sensed by the tire pressure sensor is transmitted by the transmitter to a receiver located on-board the vehicle. The tire pressure information delivered to the receiver by the RF signals from the transmitters is subsequently conveyed to a vehicle operator or occupant, typically in the form of a display.
Exemplary tire pressure monitoring systems are described and shown in U.S. Pat. Nos. 6,112,587 and 6,034,597. Conventional tire pressure monitoring systems, however, employ simplified time division multiple access (TDMA) to multiplex each tire pressure signal transmitted by the transmitters. The greatest problem associated with such TDMA tire pressure signals is that collisions between tire pressure signals can occur when multiple transmitters transmit tire pressure signals at the same time. That is, when multiple transmitters simultaneously transmit tire pressure signals, the signals overlap with each other, which can cause problems in receiving the signals, as well as in conveying accurate tire pressure information to the vehicle occupant.
Such collision problems will worsen as tire pressure monitoring systems become more common, with more and more vehicles so equipped. As more vehicles are equipped with tire pressure monitoring systems, such systems are likely to jam each other when the vehicles on which the systems are installed are within an approximate range of 20 to 30 meters from each other. That is, tire pressure signals transmitted by transmitters located in the tires of the nearby vehicles may overlap or collide, which can disrupt proper operation of the tire pressure monitoring system in each vehicle. This may be particularly problematic when such jamming occurs on the road where, for safety purposes, proper operation of a vehicle tire pressure monitoring system is especially important.
Thus, there exists a need for an improved tire pressure monitoring system and method which overcomes the tire pressure signal jamming problem described above. Such a system and method would allow for simultaneous transmission of tire pressure signals from multiple transmitters, and at the same frequency. To do so, such a system would employ spread spectrum technology, preferably through the use of code division multiple access (CDMA). According to such a system and method, the transmitters and receiver would employ CDMA so that multiple tire pressure signals transmitted simultaneously could be received by the receiver, without disruption of conveying tire pressure information to the vehicle occupant. Such a system and method would thereby provide for proper tire pressure monitoring regardless of the proximity of a vehicle equipped with the system and method to another vehicle equipped with a tire pressure monitoring system.